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The abundance of phenolic compounds (including anthocyanins) in leaves is associated with photosynthetic performance, but the regulatory mechanism is unclear. Schima superba Gardn. et Champ. and Cryptocarya concinna Hance., which exhibit distinct anthocyanin accumulation patterns, are dominant tree species in the early- and late-successional stages, respectively, of subtropical forests in China. RNA-seq and analyses of phenolic concentrations, antioxidant capacity and photosynthetic characteristics were performed on young and mature leaves of these two species under contrasting light conditions. The high-light-acclimated young leaves of S. superba and C. concinna and low-light-acclimated young leaves of C. concinna were red. These red leaves had higher ratios of electron transport rate to gross photosynthesis (ETR:Pgross) and total antioxidant capacity to chlorophyll (TAC:Chl) than did the green leaves, regardless of light conditions. In addition, the red leaves had a higher expression level of the UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) gene than did the green leaves, irrespective of light conditions. Total antioxidant capacity was positively correlated with flavonoid content in C. concinna leaves and with total phenolic content in leaves of both species under both high and low light. Consistent with the measurements of photosynthetic performance and flavonoids:Chl ratio, photosynthesis-related genes were extensively downregulated and flavonoid-pathway-related genes were extensively upregulated in young leaves relative to mature leaves. Under high and low light, both non-photochemical quenching and TAC:Chl, which serve as different types of photoprotective tools, were enhanced in young leaves of S. superba, whereas only TAC:Chl was enhanced in young leaves of C. concinna. Our results indicate that the biosynthesis of phenolic compounds in young leaves is likely enhanced by an imbalance between photosynthetic electron supply and demand and that flavonoids play a larger role in meditating photoprotection in late-successional species than in early-successional ones.

To reveal effects of elevated atmospheric CO2 on tolerance to the herbicide glyphosate in the populations of goosegrass (Eleusine indica) known to have resistance to this herbicide, two biotypes of goosegrass, a resistant (R) and a susceptible (S) biotype, were analyzed after exposed to ambient (400 μmol mol-1) and elevated CO2 (800 μmol mol-1) for 25 d. The results showed that elevated CO2 had little effect on growth of both biotypes. At elevated CO2, shoot biomass of R biotype was statistically lower than of S biotype (P<0.5). The dose-response analysis showed that glyphosate tolerance was reduced by 60% in R biotype exposed to elevated Co2 while it was slightly increased in S biotype. Elevated Co2 also had more adverse effects on photosynthetic capacity of R biotype than S biotype. As a result, maximum rate of net photosynthesis (Amax) and carboxylation efficiency (CE) under elevated CO2 in R biotype were significantly lower than in S biotype (P<0.5). These results indicate that elevated atmospheric Co2 can lead to a compromise in glyphosate tolerance of R biotype associated with poor photosynthetic characteristics, and thus will affect weed management involved with herbicide resistance in prospective agricultural systems. © 2015 Friends Science Publishers [ABSTRACT FROM AUTHOR]

The successful development of photosynthetic organs is the basis of plant growth and community development. To reveal photo-acclimation to high irradiance in tree species during the course of leaf development and plant succession of subtropical forests, photosynthetic efficiency and photoprotective compounds were analyzed in young and mature leaves of three mid-successional tree species ( Castanopsis fissa , Castanopsis chinensis and Schima superba ) and three late-successional tree species ( Machilus chinensis , Cryptocarya chinensis and Cryptocarya concinna ), grown in 100% full sunlight (FL) or 30% of FL (low light, LL). Young leaves of the two species groups exhibited lower chlorophyll (Chl) content, Rubisco content, net photosynthetic rate ( P n ), carboxylation efficiency ( CE ), effective photochemical yield ( Φ PSII ), photorespiratory electron flow ( J O ), but higher dark respiration ( R d ), and ratios of carotenoids/chlorophylls (Car/Chl), anthocyanins/chlorophylls (Anth/Chl), flavonoids/chlorophylls (Flav/Chl), phenols/chlorophylls (Phen/Chl) and total antioxidant capacity/chlorophylls (TAC/Chl) than those of mature leaves, regardless of growth irradiance. Young leaves of both species groups demonstrated a higher flexibility of Anth/Chl, Flav/Chl, Phen/Chl and TAC/Chl in response to different light conditions than mature leaves. Flav/Chl in young leaves of late-successional group was remarkably higher than that of mid-successional group under the same light conditions. There was a negative correlation between antioxidant-dependent photoprotective potential and photosynthetic efficiency in young and mature leaves of the six tree species grown under either FL or LL. Our results explain partial mechanisms that lie behind the replacement of communities in subtropical forests: highly integrated photoprotective potential allows young leaves of shade-tolerant late-successional species to develop smoothly into mature organs under high irradiance. [ABSTRACT FROM AUTHOR]